vec-iree: fix buffer unmap mechanism

Per https://github.com/google/iree/blob/main/iree/hal/buffer.h#L430,
only mapped buffer can be unmapped. Guard it with `iree_status_is_ok`
check.

Change-Id: Id997798b7e26a13eef8285100c78eb24df22d59c
1 file changed
tree: 0b07c2c991a77660042fa7fc59b4ee4082aea809
  1. cmake/
  2. samples/
  3. CMakeLists.txt
  4. springbok_config.h